There are a wide variety of injection molding systems for the molding of plastic parts by the injection of plastic under high pressure and temperature into a mold cavity. Injection molding parts which require internal threads or such protrusions or cut outs or similar defamations in the molded parts often preclude the directed straight line withdrawal of the molded plastic parts from the mold cavity of the injection-molding apparatus. If molded articles such as threaded caps are to be molded, various collapsible cores are employed, so that the core element may be withdrawn and an article with internal threads or undercuts may be easily formed. Injection molding systems employing collapsible cores are described, for example, in U.S. Pat. No. 4,456,214 issued Jun. 26, 1984 and U.S. Pat. No. 4,919,608 issued Apr. 24, 1990.
It is often desirable in injection molding systems to provide for a molded plastic article which has inward or outward projections on the external sides or surfaces of the article and optionally inward or outward projections on the internal surface of the molded object, which internal surfaces may be formed with a mandrel, such as a collapsible core, unscrewing core or straight pull out element. Typically, such molded articles may, for example, be tamper evident-sealed enclosure caps or parts with external threads or any external surface detail that precludes straight pull.
It is therefore desirable to provide for an injection molding system and method employing an expandable cavity element which will provide for the production in an efficient, effective manner of molded articles having inward and/or outward external projections on the external surface, and optionally inward or outward projections or windows on the internal surfaces as desired.